Radio frequency (RF) switches play a key role in countless electronic devices that are critical to a wide range of technologies including communications and radar systems, medical instrumentation, and consumer electronics. Switching technologies used in these systems historically involve mechanical on/off switches, and transistor or transistor-like semiconductor switching devices. For these typical switching choices trade-offs must be made among static power consumption, switch isolation, insertion loss, switching speed, required voltage bias, power handling, cost, and reliability.
Transistor and transistor-like semiconductor switching devices such as PIN diodes and varactors are commonly employed in circuits designed to interact with electromagnetic waves. PIN diodes have a superior on-off ratio and switching capability for the majority of applications when compared to varactors. However, PIN diodes require biasing and in turn much larger DC power consumption, which makes them unattractive for systems that require a significant number of switches, such as phased array antennas.
The functional process of mechanical on/off switches, such as RF MEMS switches, involves the physical motion of a conductor between two positions such that to close a circuit a physical bridge contacts two conductors and completes the conducting path of the circuit. To move the circuit into an open configuration, the bridge must be moved away from one contact to break the circuit path. While many improvements have been made in modern RF MEMS switches, the tradeoff between power handling capability and reliability is poor. RF MEMS have shown to be reliable for cold-switched and very low-power applications (>109 cycles). When hot switching is required in combination with moderate power levels, e.g. 0.1 Watts, reliability drops significantly such that RF MEMS devices are not a viable option. Also, RF MEMS switches significantly outperform PIN diodes and varactors in terms of their on-off ratio and distortion, but have many drawbacks including higher cost, lower power handling, and, for many applications, lower reliability (switching cycles before failure) due to their mechanical nature.
Each of the currently employed switches, e.g. RF MEMS and more prevalent semiconductor based devices such as PIN diodes and varactors, have significant drawbacks. Thus, any new switching technology that can improve on the currently required trade-offs will make an important impact on RF design. Despite this importance and hundreds of millions of dollars of research, there remains a need for improved switches in the RF regime.